This invention relates to a catalyst component for polymerization of alpha-olefins, and to a method of polymerizing alpha-olefins using said component. More specifically, this invention relates to a carrier-supported titanium catalyst component obtained by an improved method of preparation, and to a method for producing stereospecific homopolymers or copolymers of alpha-olefins using a catalyst composed of said catalyst component and an organoaluminum compound.
In the conventional stereospecific polymerization of alpha-olefins, solid TiCl.sub.3 is used as a catalyst component. Since only a part of titanium is utilized as catalyst, the catalytic efficiency has not been sufficiently high as to permit omission of a deashing step.
On the other hand, a method which involves dispersing and supporting a titanium compound on another solid is known as a desirable method for increasing polymerization activity per unit weight of titanium. In recent years various improved methods have been suggested about the stereospecific polymerization of alpha-olefins with a catalyst composed of a supported titanium catalyst component and an organoaluminum compound.
These improved methods are roughly classified by the method of supporting titanium, i.e., (I) copulverization of a carrier and a titanium halide, and (II) slurry supporting comprising suspending a carrier in a titanium halide and heating the suspension.
Examples of (I) include a method which comprises using a catalyst composed of a titanium catalyst component obtained by copulverizing an anhydrous magnesium dihalide and a tetravalent titanium halide or a complex of tetravalent titanium halide with an electron donor compound, and an organoaluminum catalyst component consisting of an organoaluminum compound and an electron donor compound (for example, Japanese Laid-Open Patent Publication Nos. 16986/73, 16987/73 and 16988/73); a method which comprises using a catalyst composed of a titanium catalyst component obtained by adding a halogenated silane to a magnesium alkoxide, a titanium tetrahalide and an electron donor compound and copulverizing them, and an organoaluminum catalyst component consisting of an organoaluminum compound and an electron donor compound (Japanese Laid-Open Patent Publication No. 98076/77).
The use of such catalyst systems has the advantage that the titanium compound can be effectively utilized, and the handling of these catalyst systems is convenient. However, it has the disadvantage that long periods of time are required for pulverization. Furthermore, as described in Japanese Laid-Open Patent Publication No. 16986/73, the surface area of the supported titanium catalyst component is small, and in order to omit steps of deashing and removing amorphous polymer, the results obtained are still unsatisfactory in regard to a balance between polymerization activity and stereospecificity.
Examples of (II) are a method which comprises using a catalyst composed of a supported titanium catalyst component, an organoaluminum compound and an electron donor compound, said supported titanium catalyst component being obtained by ball-milling an anhydrous magnesium halide and an electron donor compound (and a silicon compound) and contacting the resulting copulverization product with a titanium halide under heating to support titanium (Japanese Laid-Open Patent Publication No. 151691/77); a method comprising using a catalyst composed of a titanium catalyst component and an organoaluminum catalyst component, said titanium catalyst component being obtained by co-pulverizing an anhydrous magnesium halide and an electron donor compound, together with a halogenated silane (Japanese Laid-Open Patent Publications Nos. 108385/75 and 98076/77), polysiloxane (Japanese Laid-Open Patent Publication No. 20297/76) or a tin or germanium compound (Japanese Laid-Open Patent Publication No. 87489/77) prior to slurry supporting of titanium.
The methods (II) have the advantage that in catalyst preparation, supporting of titanium does not require a long period of time. On the other hand, since a large excess of titanium halide is used, they have the industrial disadvantage that steps of recovery thereof, purification, etc. are necessary. In addition, the polymerization of alpha-olefins using the aforesaid catalyst systems, especially in the presence of a molecular weight controlling agent, still poses many problems both in regard to polymerization activity and stereospecificity.
The present inventors continued extensive investigations in order to solve the aforesaid problems, and previously achieved this purpose by providing a supported titanium catalyst component obtained by (a) subjecting a magnesium halide, a tetravalent titanium halide and an organic ester to co-pulverization and/or contact treatment and heat-treating the product together with a hydrocarbon and/or a halogen-containing compound, or (b) subjecting a magnesium halide, a tetravalent titanium halide, an organic ester and a halogen-containing compound to co-pulverization and/or contacting treatment and heat-treating the product together with a hydrocarbon and/or a halogen-containing compound; and a method for polymerizing alpha-olefins characterized by using a catalyst composed of such a titanium catalyst component and an organoaluminum component consisting of an organoaluminum compound and an organic acid ester U.S. Pat. No. 4,242,230 of Ueno et al, issued Dec. 30, 1980 and U.S. Pat. No. 4,246,136 of Ueno et al, issued Jan. 20, 1981.